Re: AW: make help

[Paul Smith]

On Tue, 2015-11-17 at 07:40 +0000, Thomas Christian wrote:
> However when I add a second path to SUBDIRS variable I get the same
> error, again.
> 
> SUBDIRS := \
> src/test/usb_cdc_lolevel \
> src/module/cpu

This can't work, the way you've written your makefile.

Consider just this statement:

> > C_SRCS := \
> > $(wildcard $(DIR)$(SUBDIRS)/*.c)

Now that you have multiple subdirectories in SUBDIRS, how will make
expand this?  It will look like this:

  $(wildcard D:/test/src/test/usb_cdc_lolevel src/module/cpu/*.c)

which will run wildcard on two expressions: first
"D:/test/src/test/usb_cdc_lolevel" which presumably exists so it will
expand to just that, then "src/module/cpu/*.c" which matches nothing and
returns the empty string.

If you want to use multiple paths, you will need to use a loop or a
function like patsubst to apply the pattern to every word in the SUBDIRS
directory, like this:

  $(wildcard $(patsubst %,$(DIR)%/.c,$(SUBDIRS)))

Similarly, the rules cannot be written with multiple paths; this:

> > # Each subdirectory must supply rules for building sources it contributes
> > ./$(SUBDIRS)/%.o: $(DIR)$(SUBDIRS)/%.c

expands to:

  ./src/test/usb_cdc_lolevel src/module/cpu/%.o: 
D:/test/src/test/usb_cdc_lolevel src/module/cpu/%.c

which is again, clearly not what you want.

Unfortunately, there's no way to do a simple loop or patsubst for
defining new rules.  You'll either have to write them out by hand or
else consider a much more advanced feature such as eval.  You might read
this set of posts (start with the earliest one) but it is a very
advanced topic: http://make.mad-scientist.net/category/metaprogramming/

> To avoid running into such insidious errors, it's a good idea to
> terminate your make variables with a terminating hash

I personally just use a good programmer's text editor to edit my
Makefiles: a good text editor will provide modes you can enable that
will either remove all trailing whitespace automatically, or at least
make it visible (with color etc.)